The present invention relates generally to fuel delivery systems. More particularly, the invention relates to a system for controlling the quantity of fuel injected in a fuel injection system for an internal combustion engine. The system takes into account the fuel intake port wall wetting history and other transient conditions to achieve optimal air to fuel ratio.
Internal combustion engines operate most efficiently and with minimal pollution when the correct fuel to air ratio is maintained. This is easier said than done, because transient conditions during engine operation make it difficult to determine the precise quantity of fuel that should be injected at any given instant. In a present-day fuel injection system fuel is injected into the intake port of the fuel intake manifold. There the fuel is mixed with air and introduced into the cylinder when the intake valve is opened. Present-day fuel injection systems use microprocessor-based computer systems to determine the quantity of fuel injected into the intake manifold. Conventionally, the microprocessor-based fuel injection system monitors engine speed (RPM) and engine load (e.g., manifold pressure and manifold temperature) and the appropriate quantity of fuel is then injected based on a predetermined fuel to air ratio for the measured parameters.
The problem with conventional microprocessor-based fuel injection systems is that they do not accurately take into account what is actually happening for the fuel wall wetting in the engine during operation. When fuel is sprayed from the injector into the intake manifold, some of the fuel will deposit on the walls of the manifold as a liquid film. Although some of the fuel in the film may vaporize and thereafter enter the cylinder, the rest remains on the manifold wall and forms a liquid flow. Also, some of the unvaporized liquid fuel that enters the cylinder may not be fully burned during the combustion cycle. This unburned fuel is thus ejected as waste during the exhaust cycle and this waste fuel therefore produces no power and contributes to increased emissions. Thereafter, on subsequent cycles, some of the fuel previously deposited on the manifold wall may vaporize or migrate as a liquid and enter the cylinder, adding to the quantity of fuel injected for use during that cycle.
The net result is that the quantity of fuel that is actually consumed during the combustion on cycle will vary depending on transient operating conditions. Conventional fuel injection systems have not accurately taken this variance into account. To further complicate matters, the operator of the vehicle may, at any time, change the throttle setting (by accelerating or decelerating) or the engine load may change (going up and down hills) and this will change the instantaneous fuel requirements due to the wall wetting. Conventional microprocessor-based systems do not accurately take these transient conditions into account.
The present invention addresses these problems. The invention provides a system for controlling fuel quantity that takes into account the intake port wall wetting history to determine the precise quantity of fuel to be injected during any given cycle. The invention employs an engine speed sensor for reading the engine speed of the internal combustion engine. The system also employs an engine load sensor for reading the engine load of the internal combustion engine. Additionally, the system employs a fuel quantity selector that controls the quantity of fuel injected into the engine. A history generator, coupled to the fuel quantity selector, generates a fuel intake port wall wetting history based on parameters such as engine speed, engine temperature and engine load. The fuel quantity selector uses the fuel spray vapor fraction, the wall wetting history as well as the engine speed and engine load parameters to determine the quantity of fuel needed for the given injection cycle. By taking the wall wetting history into account for each individual cylinder, the present system is able to supply the proper quantity of fuel for each injection cycle. This results in higher efficiency and cleaner burning.
For a more complete understanding of the invention, its objects and advantages, reference may be had to the following specification and to the accompanying drawings.